The permeability characteristics of the mature iris, ciliary body, retina, and choroidal/retinal pigment epithelial complex, as shown by various methodologies, are regionally dissimilar, both in health and disease. Understanding these regional differences is important in that permeability alterations are basic parameters of the anterior and posterior ocular segments' response to disease; and, the exaggerated response of the macular to vascular permeability alterations is a critical component of macular disease. Regional permeability differences in the developing eye need to be evaluated in a systematic manner; and specifically, the developing permeability characteristics of the distinctive macular vascular system require elucidation in a foveate animal model. In this study we propose to investigate the blood-ocular permeability barriers and their regional differences in eyes of ceasarean derived monkey and cat fetuses and neonates using as a basis fluorescein labelled dextrans. These permeability markers provide selectively a wide range of molecular weights and sizes, yet they are similar in chemical characteristics. Fluorescein isothiocyanate (FITC) dextrans are covalently bound non-protein molecules that have proven useful in fluorescein angiography as determinants of molecular size in experimental in vivo permeability studies. The fluorescein marker also provides a means whereby the molecules can be localized in tissues by fluorescence microscopy; additionally, dextran molecules can be localized by transmission electron microscopy, thus facilitating the identification of their transport pathways at a subcellular level. We will use these methodologies to evaluate the developing blood-ocular barriers, thus providing a basis for better interpretation of clinical disease and for the development of more meaningful animal models.